Design and implementation of a low-cost hybrid control architecture for a 4-DOF robotic arm

The increasing demand for affordable and intelligent robotic manipulators has driven research toward hybrid control architectures that combine precision, adaptability, and real-time feedback. This paper presents the design and implementation of a four-degree-of-freedom (4-DOF) robotic arm employing a low-cost ESP32 microcontroller as the central control unit. The system integrates a hybrid Human–Machine Interface (HMI) comprising both a physical joystick and an Android-based Bluetooth application, thereby enabling flexible user interaction and redundancy in control. To enhance safety and manipulation intelligence, a Force-Sensing Resistor (FSR) was incorporated into the gripper to provide real-time force feedback, allowing adaptive grip control and preventing object damage. The mechanical subsystem was actuated using three DC geared motors and a servo motor, driven through dual L298N motor drivers, while a TFT display provided real-time feedback on control mode and sensor data. Experimental validation demonstrated that the system achieved a latency of less than 20 ms for joystick control and approximately 100-150 ms for Bluetooth control, both within acceptable operational limits. The FSR feedback effectively detected applied forces up to 4.5 N, ensuring compliant grasping of fragile and rigid objects. The results confirmed that the proposed architecture achieved high functionality, responsiveness, and user adaptability, bridging the gap between simple open-loop systems and costly industrial manipulators. The developed prototype serves as a scalable and replicable model for educational, research, and low-cost automation applications.